1. Field of the Invention
The present invention relates to a one dimensional X-ray image sensor and an X-ray inspecting apparatus using the same.
2. Description of the Related Art
Recently, there has been noticed an X-ray inspecting apparatus for measuring a content of a target material using X-ray. This utilizes such a phenomenon that the X-ray absorption coefficient of a target material differs in response to the kind of the target material and the energy of X-ray upon irradiating two kinds of X-rays having different energies to an object. For instance, when high energy and low energy X-rays are irradiated to an object comprised of materials A and B, transmissive intensities I.sub.l1 and I.sub.h1 of the low energy and high energy X-rays are given as follows. EQU I.sub.l1 =I.sub.l0 exp(-.mu..sub.la .rho..sub.a T.sub.a -.mu..sub.lb .rho..sub.b T.sub.b) (1) EQU I.sub.h1 =I.sub.h0 exp(-.mu..sub.ha .rho..sub.a T.sub.a -.mu..sub.hb .rho..sub.b T.sub.b) (2)
Wherein I.sub.l0 and I.sub.h0 are intensities of the low energy and high energy X-rays irradiated, .mu..sub.la and .mu..sub.ha are mass attenuation coefficients of the material A for the low energy and high energy X-rays, respectively, .mu..sub.lb and .mu..sub.hb are those of the material B, .rho..sub.a and .rho..sub.b are densities of the materials A and B, respectively, and T.sub.a and T.sub.b are thicknesses of the materials A and B, respectively.
From these two equations (1) and (2), the following equation is introduced. EQU T.sub.b .times..rho..sub.b ={In(I.sub.l0 /I.sub.l1).times..mu..sub.ha -In(I.sub.h0 /I.sub.h1).times..mu..sub.la }/(.mu..sub.ha .mu..sub.lb -.mu..sub.hb .mu..sub.la) (3)
From the equation, a product of the thickness T.sub.b and the density .rho..sub.b of the material B, i.e., a content of the material is obtained by measuring I.sub.l1 and I.sub.h1. For instance, the materials A and B may be soft tissue and bone tissue of the human body in bone salt (mineral) analysis, respectively. In this case, an amount of the bone tissue (T.sub.b .times..rho..sub.b) is obtained according to the equation (3) by measuring the transmissive intensities I.sub.l1 and I.sub.h1 of the low energy and high energy X-rays.
However, so called beam hardening phenomenon is inevitable in such an analysis using X-rays of different energies as mentioned above. This phenomenon is essentially based on an energy distribution of X-ray irradiated from an X-ray source. Absorption of an X-ray having an energy distribution increases as the energy thereof becomes low and the thickness of a target material increases and, accordingly, lower energy components thereof are attenuated much more than higher energy components thereof in transmission through the target material. Due to this, the effective energy of the X-ray after transmission shifts toward higher energy side as compared to that before transmission.
This beam hardening phenomenon gives influences to the mass attenuation coefficients .mu..sub.ha, .mu..sub.hb, .mu..sub.la and .mu..sub.lb since they are dependent on energies of X-ray beams passing through. Thus, the content obtained using the equation (3) is not exact.